Priority is claimed to Patent Application Numbers 2001-22978 filed in Rep. of Korea on Apr. 27, 2001 and 2002-18227 filed on Apr. 3, 2002, herein incorporated by reference.
1. Field of the Invention
The present invention relates to an evaporator having a structure for circulating working fluids by capillary action, and more particularly, to a flat evaporator having a capillarity generator that surrounds a vaporization cavity region.
2. Description of the Related Art
As electronic technologies have advanced, electronic devices tend to be designed as modules and have smaller dimensions and higher output capabilities. Heat generated per unit area of electronic devices continues to increase accordingly. Thus, it is of great concern to properly control heat generated in electronic devices in designing and operating the electronic devices. There are several well-known techniques for controlling temperature in electronic devices including: thermal conduction, natural convection/radiation or forced convection of air, cooling by a liquid, immersion, distribution of heat through heat pipes.
A capillary pumped loop (CPL), which has recently been developed, is a system in which surface tension at boundaries where phase change of a coolant occurs is used as a driving source for transporting the coolant. A cooling system employing this CPL includes an evaporator for transferring heat from a heat source using a gas coolant and a condenser for condensing the gas coolant output from the evaporator into a liquid.
CPL evaporators must be constructed such that heat generated from a heat source effectively promotes phase change of a coolant and that boundaries where phase change of the coolant occurs are evenly distributed around a heat source since surface tension at the boundaries is a driving source for transporting the coolant.
A cooling system devised by Stenger of NASA Lewis Center is constructed by a loop in which a coolant flows through a pipe. The loop consists of an evaporator portion having a porous structure that generates capillary action on a path along which the coolant flows at one end of the pipe. The loop is configured to condense the coolant by giving up heat at the other end of the pipe. Since it is difficult to make the pipe loop smaller, this structure is not suitable for electronic instruments or equipment of smaller dimensions.
U.S. Pat. No. 5,725,049 by Swanson et al., describes a flat heat exchanger employing a CPL. The heat exchanger proposed in the above patent includes an evaporator, a condenser, a liquid tube, and a vapor tube. The evaporator has top and bottom bodies, and a porous structure between the top and bottom bodies thereof. Grooves connected to the liquid tube are formed in a top portion of the porous structure, and grooves connected to the vapor tube are formed in a bottom portion thereof. The heat exchanger is configured so that a liquid coolant supplied from a central portion of the top grooves of the porous structure disperses into adjacent grooves to vaporize the liquid coolant through the porous structure thereby outputting vapor to the vapor tube through the bottom grooves thereof. However, because its structure, the heat exchanger cannot be used as a cooling device for a heat source having a small surface area but high heat generation or a small thin cooling device.
To solve the above problems, it is an object of the present invention to provide a flat evaporator having small dimensions.
It is another object of the present invention to provide a flat evaporator with small dimensions having high cooling efficiency.
Accordingly, to achieve the above objects, the present invention provides A flat evaporator comprising: a substrate having on the top surface a vaporization cavity region with a central chamber in which main evaporation of a liquid coolant occurs, a capillary region surrounding the central chamber, and a manifold region surrounding the capillary region; a top plate disposed on the substrate; a capillarity generator which is formed in the capillary region and flows the liquid coolant from the manifold region into the vaporization cavity region by capillary action; an exhaust unit which includes a gas collector and exhausts a gas coolant generated in the vaporization cavity region; a supplying unit which includes a coolant supply portion and supplies the liquid coolant from the outside to the manifold region; and an auxiliary capillarity generator having an extending portion extending towards the center of the vaporization cavity region between the top plate and the substrate.
In an alternative embodiment of the present invention, the capillarity generator may be formed of a porous body having a plurality of cavities. In another alternative embodiment, the capillarity generator may be formed of a plurality of wick structures, each having a square cross-section, densely arranged to provide a coolant flow gap between the manifold region and the vaporization cavity region.
It is preferable that the auxiliary capillarity generator has a ring-shaped body and is located on the capillarity generator. Preferably, the extending portion of the auxiliary capillarity generator is formed of a porous body capable of generating capillary action. More preferably, the entire auxiliary capillarity generator, both of the ring-shaped body and the extending portion, is formed of a porous body.
In another alternative embodiment, the auxiliary capillarity generator may be formed of an auxiliary wick structure where a ring-shaped body has an extending portion including a plurality of pins. Preferably, the pins of the auxiliary wick structure have a rectangular shape or include a circular extending portion at its rectangular front end. Preferably, the ring-shaped body of the auxiliary wick structure includes parts spaced a predetermined distance and interconnected by pins.
It is preferable that the gas collector is formed in the top plate and has a conical structure which tapers in an upward direction. Preferably, the gas collector comprises at least one stepped edge on the inner wall of the conical structure.